The present invention pertains to a method for allylating aromatic hydroxyl-containing compounds. The allyl ethers of polyphenols are useful for preparing epoxy compounds low in aliphatic halogen content.
Epoxy resins are being used in the electronics industry as components in electrical laminating varnishes, potting compositions encapsulating compositions and the like. Since aliphatic halogen atoms are detrimental to electrical properties, it is desirable to have available for the electronics industry epoxy resins which are extremely low in aliphatic halogen content. The traditional method for preparing aromatic epoxy compounds is to react an aromatic phenolic hydroxyl-containing material with an epihalohydrin and dehydrohalogenating the resultant halohydrin intermediate product with a suitable dehydrohalogenating agent such as an alkali metal hydroxide, carbonate, bicarbonate or the like. However, the resultant epoxy compound usually contains a relatively high amount of aliphatic halogen atoms of either the bound halogen type or the hydrolyzable halogen type or a combination thereof which is often referred to as total halogen content. The aromatic halogen atoms are not usually considered detrimental and are not included in the reporting of the total halogen content since in some instances, such as in electrical laminates, aromatic halogen atoms are desired so as to render the resin more flame retardant.
The present invention provides a method for preparing vicinal epoxy compounds which are very low in aliphatic halogen content rendering them particularly suitable for use in the electronics industry. These low halogen content resins are prepared by the peroxide epoxidation of allyl ethers of aromatic compounds which have been prepared by reacting an allyl halide with an alkali metal salt of an aromatic hydroxyl-containing material in the presence of a polar aprotic solvent so as to convert at least 95% of the aromatic hydroxyl groups to allyl ether groups. When protic solvents such as methanol are employed, conversions of not more than about 85% of the aromatic hydroxyl groups to allyl ether groups is obtained.